1. Field of the Invention
The present invention relates to an electronic stringed instrument, and, in particular, to an electronic stringed instrument which can generate musical tones with multifarious timbres, when played in the same typical manner as is done with traditional natural stringed instruments, such as stroking, picking and fingering stretched strings.
2. Description of the Related Art
Recently, with rapid improvement of electronic technology, electronic stringed instruments have been developed and proposed, which can generate musical tones with multifarious timbres by the same picking technique as is done with traditional natural stringed instruments. Electronic stringed instruments of this type are classified into a pitch extracting type and a string triggering type from the view points of the method to designate a musical tone to be generated and the method to generate the musical tone with a specified pitch.
According to the pitch extracting type electronic stringed instruments, the vibration frequency of a stretched string or the pitch is extracted from the vibration caused by picking the string, and the pitch of the corresponding musical tone is determined on the basis of the extracted pitch, and the musical tone with a given timbre is generated at the determined pitch when the level of the string vibration becomes greater than a predetermined value.
According to the string triggering type electronic stringed instruments, the operation position of a fret presently depressed is detected by a pitch designation operation status sensor provided on a fingerboard side, the pitch of the corresponding musical tone is designated by the sensor, the picking operation status with respect to a string is detected by a string triggering sensor provided on a body side, and a musical tone with a given timbre is generated by the string triggering sensor at the pitch designated by the former pitch designation operation status sensor. For this type of electronic stringed instruments, there are various types of pitch designation operation status sensors for detecting the fret operation position to designate the pitch of a musical tone to be generated. For instance, the following types are known:
(1) The type which has a number of ON/OFF type fret switches disposed in a matrix form in the fingerboard.
(2) The tablet coordinate detecting type.
(3) The type which has a resistance member for each string whose resistance is detected.
(4) The type which detects a string-depressed position from electric contact between a conductive string supplied with a small current and a fret contact.
(5) The type which detects the pitch by supplying an ultrasonic wave in strings and measuring the return time of the wave from a string-depressed position.
Also, there are various types of string-triggering sensors for detecting the beginning of the string vibration and designating the beginning of tone generation. They include:
(1) The magnetic pickup detecting type which magnetically detects the vibration of stretched strings.
(2) The type which detects the axial directional vibration of a string using a Hall element and a magnet.
(3) The string triggering switch type which is actuated by the vibration of a string to detect the beginning of the string vibration.
(4) The piezo-electric element detecting type which detects the string vibration using a piezoelectric element.
(5) The light pickup type which detects the string vibration from the light shielding state.
The advantage of the string triggering type electric stringed instruments over the pitch extracting type lies in their simpler structure such that the beginning of the string vibration is detected by the string triggering sensor, a musical tone is generated in response to the detection, and the pitch of the musical tone to be generated is determined by a pitch designation signal from pitch designation operation status detecting means.
On the other hand, the string triggering type has such a prominent shortcoming that musical tones generated by operating strings do not have rich musical effects or impressions. Electronic stringed instruments, as they are indeed stringed instruments, should be able to provide as rich musical impression as can be produced by traditional stringed instruments, and this is one of the important indices to be good stringed instruments. To get the index,
(A) Electronic stringed instruments should be playable in a manner very similar to the one involved in traditional stringed instruments, such as guitars, and should well respond to natural operation.
(B) The electronic stringed instruments should produce the same acoustic or musical effects as can be obtained by the traditional type when played in the same manner.
However, electronic stringed instruments which can sufficiently fulfill the above requirement are not yet available because there still are various problems that should be solved. These problems will be explained below.
According to conventional, string triggering type electronic stringed instruments, even when a fret operation position is changed during generation of a musical tone associated with a triggered string, its sound source does not respond to the change so that the frequency of the musical tone cannot be changed to the pitch corresponding to the new fret position. In other words, the conventional electronic stringed instruments have a limited function to permit generation of a single musical tone for one picking action. This significantly restricts the playing modes to such a level that the allowable playing modes or techniques, and hence the resultant musical effects, can be in no way matched with those of acoustic or electric guitars.
As a solution to this problem, some of the techniques used in keyboard type electronic instruments may be applied to the electronic stringed instruments, so that every time the fret operation position is changed, the generation of a musical tone being generated can be stopped and a new musical tone can be generated at the pitch corresponding to the new fret operation position.
With the use of such a tone generating method, however, when a string is picked with the right hand and the fret operation is done by sliding the left hand along the string during tone generation caused by the picking, a new musical tone will be generated every time the fret operation position is changed. Therefore, if, for example, the sliding (sliding the left hand along a string) is executed, the electronic stringed instruments cannot provide an effect similar to the sliding sound effect (only the pitch varying from one pitch to another) which can be produced from acoustic guitars by the sliding operation.
According to conventional stringed instruments using a string triggering switch, with respect to a string vibration above a given level, the switch temporarily becomes the ON state, which does not continue; the switch functions in a specific correlation with the string vibration. For instance, the string triggering switch does not respond to a very weak string vibration and repeatedly becomes the alternate ON/OFF state when a large vibration continues.
Therefore, when the output of the string triggering switch is directly sampled by a processor such as a microcomputer, the transition between the ON and OFF states of the switch due to the string vibration cannot be always accurately detected. For instance, at the beginning of the string vibration, even when the string triggering switch temporarily becomes the ON state, it is possible that the processor does not perform the sampling during the ON duration. At the worst, picking of a string is not detected by the processor. If not the worst, the processor may detect the picking with such a delay from the operational timing of the string that adverse musical effects are produced.
It is desirable that the beginning of tone generation coincide with the string operation timing or the beginning of the string vibration.
The above problem can be solved to some degree by sufficiently shortening the interval between samplings by the processor. This increases the burden of the processor with respect to an input device, thus requiring a simpler and assured detection of the string triggering (beginning of the string vibration).
To realize an electronic stringed instrument having a plurality of strings, the relationship between the strings and sound sources (which electronically generate musical tones) should be considered.
As one approach, one sound source may be assigned to a single string. Assume that this system is applied to the above string triggering switch type electronic string instruments. Then, when the switch detects the triggering of one string, the processor assigns one of plural sound sources to the string and instructs the sound source to start generating a musical tone at a pitch corresponding to the fret operation position, which is detected by the fret status detecting means. Consequently, the musical tone is generated from the sound source. When the same string is triggered again and the triggering is detected by the switch during generation of the musical tone from that sound source, the processor instructs the sound source to stop the tone generation and, upon completion of the tone stopping, instructs the sound source to generate the musical tone. However, the pitch for the second tone generation corresponds to the fret operation position detected by the fret status detecting means at that time. In other words, in this example, when the same string is triggered successively, the succeeding sound is generated after the previous sound is stopped.
The above approach cannot regrettably simulate the function of the sound box of a natural stringed instrument such as an acoustic guitar. According to the stringed instrument with the sound box, when the same string is successively picked, the generation of the second musical tone starts while the reverberation of the first musical tone continues. Such reverberation effect is an important property of this type of natural stringed instruments and gives a good musical impression to a listener. This desirable reverberation effect cannot be expected from the aforementioned electronic stringed instruments.
Further, according to the conventional electronic stringed instruments, the sound source selects a pitch signal from the fret switch only when supplied simply with a string triggering signal. The waveform signal with the frequency corresponding to the pitch signal is formed by a VCO element of the sound source. Meanwhile, an envelope circuit of the sound source is driven by the string triggering signal and its mode sequentially changes from attack to decay, release, etc.. The waveform signal of the above frequency is controlled by the output of the envelope circuit to provide a musical tone signal. Therefore, the continuous tone-generation time (time from the beginning of the tone generation until the end of the tone generation) is determined by the length of an envelope.
One of the functions of a synthesizer is to generate a musical tone with a number of timbres. Adding such a function to electronic stringed instruments raises problems which would not be caused in the case of electronic keyboard instruments.
One of the problems is concerned with the sound stopping control with respect to musical tones with timbres of the sustain tone system, such as an organ. The envelope for typical timbres of the sustain tone system includes a step called sustain. The sustain step has a fixed envelope value so that the musical tones of the sustain tone system are kept generated unless a sound stop instruction is sent to an envelope generator from the processor, etc. In many electronic keyboard instruments, when a key is released, a key-off signal is generated and sent to the processor, which in turn instructs the envelope generator to stop the tone generation. For instance, in an organ-sound mode, an organ sound is kept generated during depression of a key, but it is released to be stopped when the key is released.
It is regrettable that the key-off operation is not involved in traditional stringed instruments. Stringed instruments such as guitars significantly differ from keyboard instruments such as pianos and organs in mechanics and playing modes.
As one simple approach to allow the key-off operation in electronic stringed instruments, they may be designed to have a guitar-like outline but have a keyboard added to provide a key-off signal when operated. Such instruments cannot, however, be called guitars any longer and lose the natural properties of stringed instruments such as guitars. Electronic stringed instruments, as the name stands for, should have a similarity with traditional stringed instruments at least on the basic level.
According to traditional natural stringed instruments, with a string depressed by a finger of one hand, for example, the left hand, the string is stroked or picked by the right hand, causing the string vibration which generates its associated musical tone. When the finger is moved off the string, the string vibration is rapidly reduced, thus rapidly releasing the musical tone being generated. One approach to realize this phenomenon in electronic stringed instruments is to permit the instruments to electronically detect the end of the string vibration. This approach is, however, difficult to realize as it needs a string vibration sensor for accurately detecting the string vibration and some means for analyzing in real time the output of the sensor and accurately detecting the real end of the vibration while removing a spurious component included in the sensor output (for example, a phenomenon which appears as if the vibration is temporarily stopped). If realized, however, the manufacturing cost would be significantly high.
As already described earlier, with the structure of the conventional electronic stringed instruments, it is not possible to simulate the musical effect (varying only the pitch without regeneration of a new musical tone) produced by, for example, the sliding, one of guitar's basic playing techniques, according to which the fret operation position is sequentially shifted with a finger or fingers of the left hand after a string is picked by the right hand. (First simulation subject)
In acoustic guitars or the like, in addition to the sliding, a plurality of strings are generally used to play a melody. In this case, while one fret of one string is depressed with a finger of the left hand, the string is picked by the right hand, and then the finger of the left hand is moved to another string and the new string is picked by the right hand, and so forth. In the process of moving the finger of the left hand from one string to another, that finger should naturally be moved off the first string and the first string goes to the so-called open-string status. This transition to the open-string status often reduces the string vibration and this phenomenon is aurally sensed as the stopping of a sound. That is, when a finger is moved from one string to another to play a melody, the open-string pitch of the first string is not prominently audible.
Therefore, to electronically simulate such a basic phenomenon is the second simulation subject.
There still exists a difficult problem in the above case. The transition to the open-string status does not always reduce the string vibration to such a level that the phenomenon is sensed as sound stopping. For instance, when the fret status is changed from the first fret to the open-string status, it is likely that the pitch of the open string is heard following the pitch of the first fret. (If, after moving the finger of the left hand off the string, the same string is again depressed (sound stop fingering) or the string is lightly touched with a finger of the right hand, the string vibration is absorbed by the finger, so that the phenomenon can be sensed as the sound stopping.) In short, the first simulation subject contradicts the second simulation subject.
One solution to this contradiction may be to provide the electronic stringed instruments with an ability to convert the string vibration into an electric signal with a high fidelity and electrically follow up the behavior of the real string vibration in real time while removing various spurious or noise components which may be included in the converted output, whereby a sound source is properly controlled. However, this approach is difficult to realize at present, and if realized, the products would certainly be very expensive.
Natural stringed instruments such as acoustic guitars can be played distinguishing how much the string vibration should be attenuated or whether the vibration of only one string or the vibration of all the strings should be stopped, etc., by the way strings are operated with fingers of the right or left hand (for example, touching a vibrating string with a finger or a palm). It is, however, extremely difficult to electronically perform the complete simulation of the above. Even if a sensor for converting the string vibration into an electronic signal with a relatively high fidelity, an analyzing device for analyzing the output of the sensor needs to be provided with an ability to accurately follow up in real time the behavior of the string vibration, which should finally be reflected on a musical tone, while eliminating the influence of various spurious components included in the string vibration itself (signal source itself), whereby the mode of attenuating the string vibration can be distinguished, for example, through pattern matching. If the above function is realized somehow, the final products would be very expensive.
Conventionally, electronic stringed instruments have been known, which has a foot-operable fast decay pedal mounted outside the instrument main body whereby generation of a musical tone being generated can be rapidly stopped by operating the fast decay pedal with a foot, as disclosed in U.S. Pat. No. 4,336,734.
Since, in the above electronic stringed instruments, rapid stopping of the tone generation should be executed by operating the fast decay pedal disposed at a player's foot, the instruments can only be played where the fast decay pedal is disposed. This restriction does not permit the player to play the electronic stringed instruments while moving around.